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A vaccine safety study of more than 124,000 babies that appears today in the journal Pediatrics concludes there are “no consistent significant associations” between mercury-laced vaccines and maladies such as autism or attention-deficit disorder.

However, an advocacy group is accusing federal researchers of finding such a link in “earlier, secret studies” and “manipulating data” to cover it up.

“They found the truth and then swept it under the rug,” said Lyn Redwood, the mother of an autistic child and president of Safe Minds, a Cranford, N.J., organization dedicated to removing mercury from medical products.

Mercury is known to have toxic effects on the brain. Thimerosal, a mercury-containing preservative, was used for decades to stabilize vaccines. Vaccines today contain little or no thimerosal.

Rep. Dave Weldon, Florida Republican and a physician, sent a letter Friday to Dr. Julie L. Gerberding, director of the Centers for Disease Control and Prevention (CDC), asking for a “thorough, open, timely and independent review” of the study.

“I have reviewed the [Pediatrics] article and have serious reservations about the four-year evaluation and conclusions of this study,” Dr. Weldon said.

“While most childhood vaccines now have only trace amounts of mercury from thimerosal-containing vaccines, it is critical that we know with certainty if children were injured in the 1990s,” he wrote.

“I am a strong supporter of childhood vaccinations, and know that they have saved us from considerable death and suffering,” he added. However, “[W]e must fully disclose adverse events” to preserve public confidence in vaccines.

The CDC study, led by Dr. Thomas Verstraeten, was based on vaccine and health data from 124,170 infants born between 1992 and 1999 at two health maintenance organizations and 16,717 children born between 1991 and 1997 at another HMO.

The researchers found “conflicting results” about links between vaccines and tics or language delays at different sites. However, they found no evidence of significant increased risks for autism or attention-deficit disorder.

Safe Minds leaders say that, according to materials obtained through the Freedom of Information Act, Dr. Verstraeten said during the early stages of the study that he thought he saw a “plausible” link between thimerosal-containing vaccines and autism.

But, “once Dr. Verstraeten began working for vaccine manufacturer GlaxoSmithKline, he altered the data, sampling and methodology of the study so that results would point to enough inconsistencies to cast doubt” on the link, the group said.

Specifically, they said, CDC researchers added data from a Massachusetts HMO even though it had data-management problems and the state is believed to have “severely underreported” its cases of autism. This data skewed the findings, the Safe Minds leaders said.

Spokesmen for the CDC said Friday they were reviewing information about these “serious allegations.”

CDC materials say there are no proven links between autism and vaccines, and American parents and health care workers should continue to immunize babies and young children against disease.

A spokeswoman at GlaxoSmithKline referred questions about the study to the CDC, since it was conducted when Dr. Verstraeten was in an agency fellowship program.

GlaxoSmithKline is named as a defendant in lawsuits filed by persons with autism.

A spokeswoman for the Pediatrics journal said that the CDC study was “peer-reviewed by multiple experts.” Also, Dr. Verstraeten declared that he was a federal employee and had no conflict of interest when the study was performed, the journal said.